Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

Nanoparticles having a rutile-like crystalline phase and method of preparing the same

Abstract: Nanometer-sized particles comprise a mixed oxide of titanium and antimony and are characterized by rutile-like crystal phases The particles are easily prepared by hydrothemal processing, and may be used as colloids, or in various compositions and articles

Comparative study of La-Sr-Fe-O perovskite-type oxides prepared by ceramic and surfactant methods over the CH4 and H2 lean-deNOx

Abstract: Mixed oxides of the general formula La0.8Sr0.2FeO3−x were prepared by ceramic and surfactant methods and tested towards the NO/H2/O2 and NO/CH4/O2 lean-deNOx reactions in the 200–450 °C range. The materials were characterized for their bulk and surface composition by XRD, Mossbauer and XPS techniques. The main crystal phases detected were perovskites LaFeO3 and SrFeO3−x, and α-Fe2O3. The Mossbauer technique allowed the precise determination of the composition of Fe-containing phases in the solids prepared by both the ceramic and surfactant methods. Significant differences in the composition of the phases and the surface chemical states of Fe, Sr and La were revealed among the two solid compositions. For the CH4 lean-deNOx reaction at 350 °C, the La0.8Sr0.2FeO3−x solid composition (LSF-2) prepared by the surfactant method exhibited an increase by 50% in the rate of NO conversion and by 30% in the rate of N2 formation (per gram basis) as compared to the solid prepared by the ceramic method (LSF-1). An opposite relative catalytic activity behavior was observed for the two solids when tested towards the H2 lean-deNOx reaction. At 375 °C (maximum activity observed) the solid prepared by the ceramic method (LSF-1) exhibited an increase by 83% in the rate of N2 formation as compared to the solid prepared by the surfactant method (LSF-2). It is suggested that the mobility of surface lattice oxygen, the concentration of oxygen vacant sites, and the mixed valences of metal cations present in the La0.8Sr0.2FeO3−x solid all influenced by the preparation method used are the main parameters that largely influenced the catalytic behavior observed over the LSF-1 and LSF-2 solids.

Vanadium-promoted tin oxide semiconductor carbon monoxide gas sensors

Abstract: The semiconductor gas sensors investigated are constituted by vanadium-tin oxide nanoparticles, prepared by a co-precipitation method. They were evaluated for carbon monoxide detection at low temperatures. The sensing characteristics obtained are associated with the composition, structure and surface state of oxide semiconductor. XPS analysis revealed an electronic interaction between Sn and V atoms in the mixed oxide structure and the formation of vanadium cations with multiple valences. Combined XRD and FTIR analyses showed that the tin oxide crystallinity decreased with increasing vanadium loadings. Lower levels of vanadium dopants in tin oxide enhanced response to CO gas in air because they facilitated oxygen adsorption by scavenging electrons to form reactive oxygen ions on the surface, as indicated by electrical and EPR measurements. The response to CO gas in nitrogen atmosphere was observed, and increased with increasing CO concentrations. Sensing mechanisms that discuss the roles of the vanadium redox pairs and oxygen vacancies in the CO detection process are proposed.

Catalytic oxidation of methane over novel Ce–Ni–O mixed oxide catalysts prepared by oxalate gel-coprecipitation

Abstract: A novel approach for the synthesis of a new type of binary Ce–Ni–O mixed oxide catalysts is reported. The synthesis method involves the homogeneous gel-coprecipitation of oxalate precursor in alcoholic solution followed by calcinations in air. The results show that the as-prepared samples have high specific surface area and high component dispersion, exhibiting remarkably high activity in the catalytic combustion of methane as compared to the catalysts prepared by conventional coprecipitation techniques. It is suggested that the superior catalytic performance of the oxalate gel-coprecipitated Ce–Ni–O mixed oxide catalysts could be attributed to the generation of highly dispersed NiOx species and the creation of highly active oxygen vacancies as a consequence of an easier incorporation of Ni2+ ions into ceria lattice by the formation of solid solution in the mixed oxide samples.

Influence of the compensating anions of Ni/Al and Ni/Mg/Al layered double hydroxides on their activation under oxidising and reducing atmospheres

Abstract: The activities and selectivities in the hydrogenation of acetonitrile on catalysts obtained from Ni/Al and Ni/Mg/Al layered double hydroxides (LDHs) precursors depend on the nature of their compensating anions: CO2−3,NO−3 or Cl−. The latter gives rise to sample with low activity and the less selective to primary amine. Studies by XRD, TG–DSC, mass spectrometry and TPR experiments show that the anion influences the thermal stability and the reducibility of the Ni-containing LDHs. The thermal decomposition of LDH into the mixed oxide form involves the dehydration, then the dehydroxylation of the layers with the concurrent decomposition of CO2−3 and NO−3 which occurs at similar temperature in air or H2 atmosphere. In TPR experiments the reduction of Ni2+ to Ni0 takes place at above 800 K. A specific behaviour is observed when Cl− is the compensating anion, with a better reducibility of Ni2+ and the existence of Ni species reduced at low temperatures, not observed with CO2−3 and NO−3 as anions. In addition, all the mixed oxides are poorly reconstructed in water, and a clear segregation of bayerite occurs on the chloride samples. This last phenomenon is enhanced in the Mg-containing compound. It is proposed that the presence of both Cl and Mg favours the extraction of aluminium and makes the accessibility to a significant amount of Ni2+ cations easier, thus increasing their reducibility. In this case, Ni0 particles with an average size around 65 nm are detected after reduction at 723 K, while the other samples, poorly reduced, still contain the mixed oxide structure.